The movement of natural gas in a gathering system pipeline poses a major problem when the gas cools to ground temperature, causing heavy hydrocarbons to condense to the liquid phase. The condensate collects in draws, low points in the line, creating pressure loss as the gas attempts to lift the condensate fluid. As the quantity of fluid increases, pressure loss increases consequently reduce the quantity of gas that can be transported in the pipeline. When condensate fluid is present in enough quantity to "trap" a draw, the gas flow will raise the fluid until it can break free. After the gas flows by the fluid, the fluid will have a tendency to descend back into the draw. This back and forth fluid action can continue for extensive periods of time and can cause mechanical erosion of the pipeline in the low area. Any water present in the fluid will promote chemical corrosion in the pipeline, depositing corrosion products which build up and promote the corrosion process. In order to remove this condensate liquid from the draws, it is common pipeline practice to utilize the force of the moving gas to force a spheroid through the line causing the pressure of the gas stream to move it. The spheroid, or ball pig, actually forces the condensate out of the line and thus prevents it from flowing back into the draw by gravity action.
A spheroid, or ball pig, has many major disadvantages when compared with a cup pig. A ball pig is commonly formed from hollow rubber or elastomer shells which are filled under presssure with fluid to establish the outside diameter of the ball. Inside the pipeline, the ball can be deformed by the gas pressure, allowing gas and condensate to slip by the ball pig or spheroid and flow back into the low area. In such case obviously a ball pig only removes a part of the condensate from the line which results in the necessity for frequent pigging in order to keep the flow line reasonably clear. The ball pig has only one circular point of contact with the flow line, affording a poor sealing system. Ball pigs also tend to hang up in the system, resulting in unreliable receiving frequency, even with flawless launching. In comparison, cup pigs can have five or more circular points of contact with the flow line, with gas pressure actually forcing the cups to expand radially outwardly against the inner surface of the pipeline, thereby forming an excellent seal. The cups of the pig can expand or contract as necessary to compensate for small changes in pipeline diameter. Cup pigs are typically enabled to move easily through telescoped pipelines, short radius welled ells, mitered joints, tees, valves, dents and deformed pipe without becoming lodged in the system. The advanced sealing of cup pigs is particularly important when a cup pig is utilized to separate dissimilar fluids being transported in the same pipeline. The major advantage of ball pigs is the large number of ball launching and receiving devices that are commercially available for inserting the ball pigs into the pipeline and subsequently removing them from the pipeline. There is a need in the industry for an efficient mechanism to launch and receive cup pigs, manually or automatically, thus allowing their use in a wider range of pipeline applications. The present invention is therefore directed to a mechanism for launching and retrieving cup pigs, which mechanism is capable of being operated manually or automatically according to the desires of the user.